Imaging apparatus

ABSTRACT

An apparatus for improving electrophoretic imaging by filling the space between the electrodes of the electrophoretic imaging system with an insulating liquid, then contacting the suspension with the electrode and applying an electric field for imaging.

United States Patent Leonard M. Carreira Pentield, N.Y.

May 5, 1969 Division of Ser. No. 519,034, Jan. 6, 1966, Pat. No.3,485,738

June 1, 1971 Xerox Corporation Rochester, NY.

Inventor Appl. No. Filed Patented Assignee IMAGING APPARATUS 5 Claims, 1Drawing Fig.

U.S. Cl 355/3, 96/1 G03g 15/00 Field of Search 355/3, 4;

[56] References Cited UNITED STATES PATENTS 2,975,052 3/1961 Fotland etal.... 96/1 3,394,002 7/1968 Brickmore .l 96/1 3,447,922 6/1969Weinberger 96/l (X) Primary Examiner-Samuel S. Matthews AssistantExaminer-Robert P. Greiner Anarneys-Paul M. Enlow, James J. Ralabate,Norman E.

Schrader, Ronald Zibelli and Barry J. Kesselman ABSTRACT: An apparatusfor improving electrophoreticimaging by filling the space between theelectrodes of the electrophoretic imaging system with an insulatingliquid, then contacting the suspension with the electrode and applyingan elec tric field for imaging.

PATENTED JUN 1 I97! INVENTOR. LEONARD M. CARREIRA IMAGING APPARATUS Thisis a division of application Ser. No. 519,034, filed Jan. 6, 1966, andnow U.S. Pat. No. 3,485,738 issued on Dec. 23, 1969.

This invention relates in general to imaging systems and, morespecifically, to an improved electrophoretic imaging system.

There has been recently developed an electrophoretic imaging systemcapable of producing color images which utilizes electricallyphotosensitive particles. This process is described in detail andclaimed in U.S. Pat. Nos. 3,384,565; 3,384,566 and 3,383,993 all issuedon May 21, 1968. In such an imaging system, variously coloredlight-absorbing particles are suspended in a nonconductive liquidcarrier. The suspension is placed between electrodes, subjected to apotential difference and exposed to an image. As these steps arecompleted, selected particle migration takes place in imageconfiguration, providing a visible image at one or both of theelectrodes; An essential component of the system is the suspendedparticles which must be electrically photosensitive and which apparentlyundergo a net change in charge polarity upon exposure to activatingelectromagnetic radiation, through interaction with one of theelectrodes. In a monochromatic system, particles of a single color areused, producing a single colored image equivalent to conventionalblack-and-white photography. [n a polychromatic system, the images areproduced in natural color because mixtures of particles of two or moredifferent colors which are each sensitive only to light of a specificwavelength or narrow range of wavelengths are used. Particles used inthis system must have both intense and pure colors and be highlyphotosensitive.

Ordinarily, electrophoretic imaging systems include a transparent,conductive injecting electrode upon which the dispersion ofphotosensitive particles in an insulating liquid is coated. The image tobe reproduced is projected on the suspension to the injecting electrode.During exposure, a potential, usually of from 300 to 2,000 volts isimposed on the suspension between the injecting electrode and arelatively insulating blocking electrode. This blocking electrode,ordinarily in the form of a roller or an endless belt, consists of aconductive core with an insulating surface. This blocking electrode ispassed across the surface of the liquid suspension during exposure.Unwanted photosensitive particles migrate to the surface of the blockingelectrode, leaving an image on the injecting electrode corresponding tothe original.

It has often been found that images produced by the system broadlydescribed above have uneven density and are blotchy or mottled inappearance. It is theorized that the uneveness in the image is caused byvarying corona discharge or air ionization between the blockingelectrode and the injecting electrode as the blocking electrodeapproaches the particle suspension. While the system described above isoften capable of producing excellent images, at times, especially duringperiods of high relative humidity, the images produced are not ofcommercially acceptable quality. Thus, there is a continuing need forimprovements in image quality under all ambient conditions.

It is, therefore, an object of this invention to provide anelectrophoretic imaging system which is devoid of the abovenoteddisadvantages.

It is another object of this invention to provide a method ofeliminating varying corona discharge or air ionization betweenelectrodes in electrophoretic imaging systems.

It is another 'object of this invention to provide an electrophoreticimaging system capable of producing images of uniform density undervaried humidity conditions.

The foregoing objects and others are accomplished in accordance withthis invention by filling the air gap between the electrodes in anelectrophoretic imaging system with an insulating liquid before theelectrodes are brought into proximity in the image-forming area. Theinsulating liquid may comprise any material which is sufficientlyinsulating to prevent corona discharge between the electrodes and whichis compatible with the insulating liquid in which the imaging particlesare suspended. Preferably, the liquid should have a resistivity of about10" ohm/cm. or greater. It is also preferred that the liquid have thesame general composition as the carrier liquid which the photosensitiveparticles are suspended to ensure compatibility should some of thisliquid be carried by the roller into the imaging area. Suitableinsulating liquids include Sohio Odorless Solvent 3440 (a kerosenefraction available from Standard Oil of Ohio), lsopar G (a longchain-saturated aliphatic hydrocarbon available from Humble Oil Companyof New Jersey), Freon (a fluorinated hydrocarbon available from E. l. DuPont de Nemours and Company), Fluorochemical FC-75 (a polyfluorinatedmixture of compounds containing eight carbon atoms, available fromMinnesota Mining and Manufacturing Co.), Silicon Fluid SF-96 (a dimethylsilicane fluid available from General Electric), mineral oil, decane,dodecane, N -tetradecane, molten paraffin, molten beeswax or othermolten thermoplastic material. Any other suitable insulating liquid maybe used where desired.

The advantages of this improved electrophoretic imaging system willbecome further apparent upon consideration of the following detaileddisclosure of the invention; especially when taken in conjunction withthe accompanying drawing which shows a side view of a simple exemplaryfor carrying out the process of this invention.

Referring now to the FIGURE, there is seen a transparent electrodegenerally designated 1 which, in this exemplary instance, is made up ofa layer of optically transparent glass 2 overcoated with a thinoptically transparent layer 3 of tin oxide, commercially available underthe name NESA glass. This electrode shall hereafter be referred to asthe injecting electrode. Coated on the surface of injecting electrode 1is a thin layer 4 of finely divided photosensitive particles disposed inan insulating liquid carrier. The term photosensitive" for the purposeof this invention, refers to the properties of a particle which, oneattracted to the injecting electrode, will migrate away from it underthe influence of an applied electric field when it is exposed to actinicelectromagnetic radiation. For a detailed theoretical explanation of theapparent mechanism of operation of this imaging process, see the abovementioned U.S. Pats. Nos. 3,384,565; 3,384,566 and 3,383,993, thedisclosures of which are incorporated herein by reference. Adjacent tothe liquid suspension 4 is a second electrode 5 hereinafter called theblocking electrode, which is connected to one side of the potentialsource 6 through a switch 7. The opposite side of potential source 6 isconnected to the injecting electrode 1 so that when switch 7 is closed,an electric field is applied across the liquid suspension 4 betweenelectrodes l and 5 as blocking electrode 5 passes over liquid suspension4. An image projection made up of light source 8, a transparency 9, anda lens 10 is provided to expose the dispersion 4 to a light image of theoriginal transparency 9 to be reproduced. Electrode 5 is made in theform of a roller having a conductive central core 11 connected to thepotential source 6, The core is covered with a layer of a blockingelectrode material 12, which may be Baryta paper or other suitableinsulating material. The blocking electrode may, of course, be in anyother configuration capable of contacting the suspension withoutrelative movement at the suspension surface. Typical alternativeconfigurations are described in copending application Ser. No. 452,651,filed May 3, 1965. The particle suspension is exposed to the image to bereproduced while potential is applied across the blocking and injectingelectrodes by closing switch 7. Roller 5 is caused to roll across thetop surface of injecting electrode 1 with switch 7 closed during theperiod of image exposure. This light exposure causes exposed particlesoriginally attracted to electrode 1 to migrate through the liquid andadhere to the surface of the blocking electrode 5, leaving behind apigment image on the injecting electrode surface which is a duplicate ofthe original transparency 9. After exposure, the relatively volatilecarrier liquid evaporates off, leaving behind the image. This process,utilizing only components exemplified by those discussed above, is initself, capable of ordinarily producing good images. However, undercertain circumstances, such as high humidity the image produced tends tohave variable density and a mottled or blotchy appearance. it has beenfound that this problem may be overcome by providing an applicator means13 to apply an insulating liquid to the surface of the blockingelectrode forming a pool at 14 which fills the gap between blockingelectrode 5 and injecting electrode 1 until blocking electrode 5 reachesdispersion. The gap-filling insulating liquid may be applied by anyconvenient method, For example, the liquid may be applied by spray ordropper to the blocking electrode surface or to the injecting electrodesurface at a location so as to fill the space between the electrodes.Where the. particle suspension is, alternatively, coated onto theroller-blocking electrode instead of the injecting electrode, thecorona-preventing liquid may be applied to the injecting electrode,either by moistening the entire surface of the injecting electrode or byforming a pool at the gap between the electrodes. It appears that thisgap-filling insulating liquid prevents corona discharge or airionization between electrodes 5 and 1 and thus eliminates disruption ofthe image.

Any suitable insulating liquid may be used as the carrier for thephotosensitive particles in this system. Typical carrier materials aredecane, dodecane, N-tetradecane, paraffin, beeswax or otherthermoplastic materials, Sohio Odorless Solvent 3440, (a kerosenefraction available from Standard Oil Company of Ohio) and lsopar-G (along chain saturated aliphatic hydrocarbon available from Humble OilCompany of New Jersey). i

As discussed-above, any suitable insulating liquid may be used to fillthe gap between the injecting and blocking electrodes. Good qualityimages have been produced with voltages ranging from 300 to 5,000 volts,in the apparatus of the FIGURE.

The following examples further specifically define the present inventionwith respect to the use of an insulating liquid between the electrodesbefore imaging in an electrophoretic imaging system. Parts andpercentages are by weight unless otherwise indicated. The examples beloware intended to illustrate various preferred embodiments of the presentinvention.

All of the following examples are carried out in an apparatus of thegeneral type illustrated in the FIGURE with the particle mix 4 coated ona NESA glass substrate through which exposure is made. The NESA glass isconnected in series with a switch, a potential source, and theconductive center of a roller having a coating of Baryta paper on itssurface. The roller is approximately 2 /;inches in diameter and is movedacross the plate surface at about 1.45 centimeters per second. The plateemployed is roughly 3 inches square and is exposed to a light intensityof about 8,000 foot candles as measured on the uncoated NESA glasssurface. The suspension is exposed to -an image by means of aconventional transparency. Examples l-V use a black-and-whitetransparency and produce monochromatic images. Examples Vl-X use aKodachrome" transparency and produce full color images. All pigmentswhich have a relatively large particle size as received commercially oras made are ground in a ball mill for 48 hours to reduce their size toprovide a more stable dispersion which improves the resolution of thefinal images.

EXAMPLE I About 8 parts of 2, 4, 6-tris(3-pyrenylazo) phloroglucinol ismixed with about 100 parts Sohio Odorless Solvent 3440. This dispersionis coated onto the NESA glass substrate. No liquid is introduced intothe gap between the roller electrode and the NESA glass substrate;leaving a small air gap therebetween. Relative humidity is measured andis found to be about 35 percent. A potential of about 2500 volts isimposed on the roller electrode during exposure. After exposure, animage corresponding to the original is seen on the NESA surface and anegative image is seen on the Baryta surface of the roller electrode.The positive image is of excellent quality but with slight variations indensity across the image surface.

EXAMPLE n The imaging process of Example I is repeated, except thatsufficient Sohio Odorless Solvent 3440 is applied to the rollerelectrode before imaging to fill the air gap between the rollerelectrode and the NESA glass substrate before the potential is appliedbetween the electrodes. After exposure, an excellent image correspondingto the original is observed on the NESA surface. Resolution and contrastare equal to that produced in Example I and image density is somewhatmore uniform across the image surface.

EXAMPLE Ill The imaging process of Example I is repeated, however, therelative humidity is maintained at about 85 percent. An image of goodquality but with severe variations in density and a mottled and blotchyappearance results.

EXAMPLE IV The imaging process of Example III is repeated, except thatsufficient Sohio Odorless Solvent 3440 is applied to the surface so asto fill the air gap between the roller electrode and the NESA surfacebefore potential is applied across said electrodes. The image producedis of excellent quality with much improved image density uniformity.

EXAMPLE V The imaging process of Example IV is repeated, except Isopar-Gis applied to the blocking electrode surface instead of the SohioOdorless Solvent 3440. The image produced is of excellent quality withvery uniform density across the image surface.

EXAMPLE VI A pigment mix is prepared comprising equal parts of a yellowpigment, Algol Yellow GC, 1, 2, 5, 6-di(C, C'-diphenyl)-pyrazol-anthraquinone, C.l. No. 67300, available from General Dyestuffs;a magneta pigmnet, Locarno Red X-l686, l-(4-methyl-5'-phyloroazobenzene-2 '-sulfonic acid )-2- hydroxy-3-naphthoic acid,C.l. No. 15865, available from American Cyanamid; cyan pigment, a cyanpigment, Monolite Fast Blue GS, a mixture of alpha and beta forms ofmetal-free phthalocyanine, available from Arnold Hoffman Company. About8 parts of this mixture is dispersed in about 100 parts lsopar-G and thesuspension is coated onto the NESA glass substrate. No liquid is appliedto the roller electrode surface,

I leaving an air gap between the roller electrode and the NESA glasssubstrate. Ambient relative humidity is about 40 percent. A potential ofabout 2500 volts is imposed on the roller electrode during exposure.After exposure, a full color image corresponding to the original is seenon the NESA surface. This image is of excellent quality, however, thereis a noticeable variation in image density across the image surface.

EXAMPLE VII The imaging process of Example Vl is repeated, except thatsufficient Sohio Odorless Solvent 3440 is applied to the rollerelectrode surface so as to fill the gap between the roller electrode andthe NESA glass substrate before potential is applied across theelectrodes. Again, the image produced is of excellent quality. Here,however, image density is uniform across the image surface.

EXAMPLE VIII The imaging process of Example V1 is repeated, except thatambient relative humidity is maintained at about percent. The imageproduced is of satisfactory quality; but with severe variations in imagedensity across the image surface, giving a blotchy or mottled appearanceto the image.

EXAMPLE IX The imaging process of Example VIII is repeated, except thatsufiicient Sohio Odorless Solvent 3440 is applied to the rollerelectrode surface so as to fill the air gap between the roller electrodeand the NESA glass substrate before a potential is applied across theelectrodes. The image produced is of excellent quality with very littlevariation in image density across the image surface.

EXAMPLE x The imaging process of example IX is repeated, except that theliquid applied to the roller electrode surface to fill the air gap isdecane, instead of Sohio Odorless Solvent 3440. Again, an excellentimage is produced with little variation of density across the imagesurface.

Although specific components and proportions have been described in theabove examples, relating to electrophoretic imaging, other suitablematerials, as listed above, may be used with similar results. Inaddition, other materials may be added to the gap filling insulatingliquid or to the particle suspension to synergize, enhance, or otherwisemodify their properties. For example, the particle dispersions may bedye sensitized or electrically sensitized, if desired, or may be mixedor otherwise combined with other photosensitive materials, both organicand inorganic.

Other modifications and ramifications of the present invention willoccur to those skilled in the art upon a reading of the presentdisclosure. These are intended to be included within the scope of thisinvention.

What I claim is:

1. An apparatus for electrophoretic imaging comprising:

a. at least twoelectrodes, at least one of which is a blocking electrodemovable relative to said other electrode,

b. a suspension of photosensitive pigment in a liquid carrier on a firstportion of said other electrode,

c. means to fill a gap between said blocking electrode and a secondportion of said other electrode with an insulating liquid,

d. means to apply an electric field between said electrodes,

and

e. means to simultaneously project an image on said suspension and tomove said blocking electrodes relative to said other electrode incontact with said suspension.

2. The apparatus of claim 1 wherein one of said electrodes is at leastpartially transparent.

3. An apparatus for electrophoretic imaging comprising in combination:

a. a first electrode having a suspension of a photosensitive pigment ina liquid carrier maintained on a first portion thereof,

b. a second electrode capable of being a blocking electrode maintainedin near contact with a second portion of said first electrode therebyproviding a gap therebetween,

c. means to present an insulating liquid in a gap between said secondelectrode and a second portion of said first electrode,

d. means to apply an electric field between said electrodes,

and

e. means to simultaneously project an image on said suspension and tomove said second electrode relative to said first electrode in contactwith said suspension.

4. The apparatus of claim 1 further including means to move saidelectrodes relative to each other such that said second electrodecontacts the suspension on said first portion of said first electrodewhile maintaining the insulating liquid therebetween.

5. Apparatus for electrophoretic imaging comprising in combination:

a first electrode capable of supporting a suspension of photosensitivepigment in a liquid carrier on a surface thereof, a second electrodecapable of being a blocking electrode maintained in at least nearcontact with said first electrode and being shaped for providing a nipbetween said electrodes,

means to present an insulating liquid at the entrance to the nip betweensaid electrodes,

means to move said electrodes relative to each other whereby thesurfaces of the electrodes are traversed by the nip formed therebetween,

means to simultaneously apply an electric field between said electrodes,and

means to project an image on said suspension during the traversingmovement of said electrodes.

2. The apparatus of claim 1 wherein one of said electrodes is at leastpartially transparent.
 3. An apparatus for electrophoretic imagingcomprising in combination: a. a first electrode having a suspension of aphotosensitive pigment in a liquid carrier maintained on a first portionthereof, b. a seconD electrode capable of being a blocking electrodemaintained in near contact with a second portion of said first electrodethereby providing a gap therebetween, c. means to present an insulatingliquid in a gap between said second electrode and a second portion ofsaid first electrode, d. means to apply an electric field between saidelectrodes, and e. means to simultaneously project an image on saidsuspension and to move said second electrode relative to said firstelectrode in contact with said suspension.
 4. The apparatus of claim 1further including means to move said electrodes relative to each othersuch that said second electrode contacts the suspension on said firstportion of said first electrode while maintaining the insulating liquidtherebetween.
 5. Apparatus for electrophoretic imaging comprising incombination: a first electrode capable of supporting a suspension ofphotosensitive pigment in a liquid carrier on a surface thereof, asecond electrode capable of being a blocking electrode maintained in atleast near contact with said first electrode and being shaped forproviding a nip between said electrodes, means to present an insulatingliquid at the entrance to the nip between said electrodes, means to movesaid electrodes relative to each other whereby the surfaces of theelectrodes are traversed by the nip formed therebetween, means tosimultaneously apply an electric field between said electrodes, andmeans to project an image on said suspension during the traversingmovement of said electrodes.